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## 5-1

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**5-1**Identifying Linear Functions Holt Algebra 1 Warm Up Lesson Presentation Lesson Quiz Holt McDougal Algebra 1**Warm Up**1. Solve2x –3y = 12 for y. 2. Graph forD:{–10, –5, 0, 5, 10}.**Objectives**Identify linear functions and linear equations. Graph linear functions that represent real-world situations and give their domain and range.**Vocabulary**linear function linear equation**The graph represents a function because each domain value**(x-value) is paired with exactly one range value (y-value). Notice that the graph is a straight line. A function whose graph forms a straight line is called a linear function.**Example 1A: Identifying a Linear Function by Its Graph**Identify whether the graph represents a function. Explain. If the graph does represent a function, is the function linear? Each domain value is paired with exactly one range value. The graph forms a line. linear function**Example 1B: Identifying a Linear Function by Its Graph**Identify whether the graph represents a function. Explain. If the graph does represent a function, is the function linear? Each domain value is paired with exactly one range value. The graph is not a line. not a linear function**Example 1C: Identifying a Linear Function by Its Graph**Identify whether the graph represents a function. Explain. If the graph does represent a function, is the function linear? The only domain value, –2, is paired with many different range values. not a function**Check It Out! Example 1a**Identify whether the graph represents a function. Explain. If the graph does represent a function, is the function linear? Each domain value is paired with exactly one range value. The graph forms a line. linear function**Check It Out! Example 1b**Identify whether the graph represents a function. Explain. If the graph does represent a function, is the function linear? Each domain value is paired with exactly one range value. The graph forms a line. linear function**Check It Out! Example 1c**Identify whether the graph represents a function. Explain. If the graph does represent a function, is the function linear? Each domain value is not paired with exactly one range value. not a function**You can sometimes identify a linear function by looking at a**table or a list of ordered pairs. In a linear function, a constant change in x corresponds to a constant change in y.**The points from this table lie on a line.**In this table, a constant change of +1 in x corresponds to constant change of –3 in y. These points satisfy a linear function.**The points from this table do not lie on a line.**In this table, a constant change of +1 in x does not correspond to a constant change in y. These points do not satisfy a linear function.**x**y +4 +4 +4 +4 +3 +3 +3 +3 Example 2A: Identifying a Linear Function by Using Ordered Pairs Tell whether the set of ordered pairs satisfies a linear function. Explain. {(0, –3), (4, 0), (8, 3), (12, 6), (16, 9)} Write the ordered pairs in a table. Look for a pattern. 0 4 8 12 16 –3 0 3 6 9 A constant change of +4 in x corresponds to a constant change of +3 in y. These points satisfy a linear function.**x**y +2 +2 +2 +2 –12 –4 +4 +12 Example 2B: Identifying a Linear Function by Using Ordered Pairs Tell whether the set of ordered pairs satisfies a linear function. Explain. {(–4, 13), (–2, 1), (0, –3), (2, 1), (4, 13)} Write the ordered pairs in a table. Look for a pattern. –4 –2 0 2 4 13 1 –3 1 13 A constant change of 2 in x corresponds to different changes in y. These points do not satisfy a linear function.**x**y +2 +2 +2 +2 –1 –1 –1 –1 Check It Out! Example 2 Tell whether the set of ordered pairs {(3, 5), (5, 4), (7, 3), (9, 2), (11, 1)} satisfies a linear function. Explain. Write the ordered pairs in a table. Look for a pattern. 3 5 7 9 11 5 4 3 2 1 A constant change of +2 in x corresponds to a constant change of –1 in y. These points satisfy a linear function.**Another way to determine whether a function is linear is to**look at its equation. A function is linear if it is described by a linear equation. A linear equation is any equation that can be written in the standard form shown below.**Notice that when a linear equation is written in standard**form • x and y both have exponents of 1. • x and y are not multiplied together. • x and y do not appear in denominators, exponents, or radical signs.**For any two points, there is exactly one line that contains**them both. This means you need only two ordered pairs to graph a line.**x = 2y + 4**–2y –2y x –2y = 4 Example 3A: Graphing Linear Functions Tell whether the function is linear. If so, graph the function. x = 2y + 4 Write the equation in standard form. Try to get both variables on the same side. Subtract 2y from both sides. The equation is in standard form (A = 1, B = –2, C = 4). The equation can be written in standard form, so the function is linear.**•**• • Example 3A Continued x = 2y + 4 Plot the points and connect them with a straight line. To graph, choose three values of y, and use them to generate ordered pairs. (You only need two, but graphing three points is a good check.)**Example 3B: Graphing Linear Functions**Tell whether the function is linear. If so, graph the function. xy = 4 This is not linear, because x and y are multiplied. It is not in standard form.**y = 5x – 9**–5x –5x –5x + y = – 9 Check It Out! Example 3a Tell whether the function is linear. If so, graph the function. y = 5x – 9 Write the equation in standard form. Try to get both variables on the same side. Subtract 5x from both sides. The equation is in standard form (A = –5, B = 1, C = –9). The equation can be written in standard form, so the function is linear.**•**• • Check It Out! Example 3a Continued y = 5x – 9 To graph, choose three values of x, and use them to generate ordered pairs. (You only need two, but graphing three points is a good check.) Plot the points and connect them with a straight line.**Check It Out! Example 3b**Tell whether the function is linear. If so, graph the function. y = 12 The equation is in standard form (A = 0, B = 1, C = 12). The equation can be written in standard form, so the function is linear.**y**Check It Out! Example 3b Continued y = 12**Check It Out! Example 3c**Tell whether the function is linear. If so, graph the function. y = 2x This is not linear, because x is an exponent.**For linear functions whose graphs are not horizontal, the**domain and range are all real numbers. However, in many real-world situations, the domain and range must be restricted. For example, some quantities cannot be negative, such as time.**Sometimes domain and range are restricted even further to a**set of points. For example, a quantity such as number of people can only be whole numbers. When this happens, the graph is not actually connected because every point on the line is not a solution. However, you may see these graphs shown connected to indicate that the linear pattern, or trend, continues.**x**f(x) = 7x 1 f(1) = 7(1) = 7 2 f(2) = 7(2) = 14 f(3) = 7(3) = 21 3 Example 4: Application An approximate relationship between human years and dog years is given by the function y = 7x, where x is the number of human years. Graph this function and give its domain and range. Choose several values of x and make a table of ordered pairs. The number of human years must be positive, so the domain is {x ≥ 0} and the range is {y ≥ 0}.**(3,21)**x f(x) = 7x • 1 f(1) = 7(1) = 7 • (2,14) 2 f(2) = 7(2) = 14 • (1,7) f(3) = 7(3) = 21 3 Example 4 Continued An approximate relationship between human years and dog years is given by the function y = 7x, where x is the number of human years. Graph this function and give its domain and range. Graph the ordered pairs.**Check It Out! Example 4**What if…? At a salon, Sue can rent a station for $10.00 per day plus $3.00 per manicure. The amount she would pay each day is given by f(x) = 3x + 10, where x is the number of manicures. Graph this function and give its domain and range.**f(x) = 3x + 10**x 0 f(0) = 3(0) + 10 = 10 1 f(1) = 3(1) + 10 = 13 2 f(2) = 3(2) + 10 = 16 f(3) = 3(3) + 10 = 19 3 4 f(4) = 3(4) + 10 = 22 f(5) = 3(5) + 10 = 25 5 Check It Out! Example 4 Continued Choose several values of x and make a table of ordered pairs. The number of manicures must be a whole number, so the domain is {0, 1, 2, 3, …}. The range is {10.00, 13.00, 16.00, 19.00, …}.**The individual points are solutions in this situation. The**line shows that the trend continues. Check It Out! Example 4 Continued Graph the ordered pairs. ($)**Lesson Quiz: Part I**Tell whether each set of ordered pairs satisfies a linear function. Explain. 1. {(–3, 10), (–1, 9), (1, 7), (3, 4), (5, 0)} No; a constant change of +2 in x corresponds to different changes in y. 2. {(3, 4), (5, 7), (7, 10), (9, 13), (11, 16)} Yes; a constant change of +2 in x corresponds to a constant change of +3 in y.**Lesson Quiz: Part II**Tell whether each function is linear. If so, graph the function. 3. y = 3 – 2x no yes 4. 3y = 12**Lesson Quiz: Part III**5. The cost of a can of iced-tea mix at Save More Grocery is $4.75. The function f(x) = 4.75x gives the cost of x cans of iced-tea mix. Graph this function and give its domain and range. D: {0, 1, 2, 3, …} R: {0, 4.75, 9.50, 14.25,…}